


Margin of Error

by idiopathicsmile



Category: Brooklyn Nine-Nine (TV)
Genre: F/F
Language: English
Status: Completed
Published: 2015-12-20
Updated: 2015-12-20
Packaged: 2018-05-07 21:46:18
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 7,547
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5471792
Author URL: https://archiveofourown.org/users/idiopathicsmile/pseuds/idiopathicsmile
Summary: <blockquote class="userstuff">
              <p>Amy had this thing where she did stuff that normally would’ve annoyed the hell out of Rosa, except it didn’t annoy Rosa at all. Which was confusing. Also, annoying.</p>
            </blockquote>





	Margin of Error

**Author's Note:**

  * For [bookgazing](https://archiveofourown.org/users/bookgazing/gifts).



It all started when Gina found Amy washing her socks in the break room sink before work.

“Amy, for shame!” shouted Boyle, when Gina announced it at the end of a departmental meeting. “I make soup in there!”

“In the _sink_?” said Rosa.

Boyle turned around in his chair. “I’ve had three different crock pots stolen out of that room,” he explained. “At some point I had to get creative.”

“Or just—y’know, not make giant vats of soup at work,” said Jake.

“People, we are losing sight of the issue here,” said Gina, waving her arms. “Which is shaming Amy for her _disgusting_ habits, and comforting me, for witnessing a sight so appalling, so horrifying, as to be _nigh-Hitchcockian_ —”

“Joke’s on you,” said Scully smugly. “Me and Hitchcock haven’t washed our socks in _months_.”

Scully and Hitchcock high-fived. “No,” said Terry, “that is not a high five moment—”

“Okay, I confess!” said Amy, caving to whatever atom of pressure she must have sensed in the room, like a canary in a mine. “I was doing laundry in the break room, but only because it’s not safe for me in my building right now—”

“What,” said Rosa.

“Why,” said Gina, “did you get caught up in some kind of turf war? _Talbots vs. Land’s End, whose beige is more neutral_?”

“No,” Amy said. “There was. An incident. With my upstairs neighbor.”

It turned out Amy lived below a hoarder. The hoarder’s specialties were unregulated Soviet-era waterbeds and feral cats.

Jake leaned forward hopefully. “With...hilarious results?”

“Over the weekend, the cats got in a fight and broke open four of the waterbeds,” Amy conceded, rubbing her forehead.

“Haha,” said Jake.

“But the liquid inside was infected—"

“Ew,” said Jake.

“—with something called Estonian Fighting Mold—”

“Ooh!” said Jake.

“Which is a highly aggressive airborne spore that gives people permanent nerve damage.”

“...not totally sure what noise to make here,” Jake admitted.

“So I’m trying not to go back to my place too much until they get it cleaned out.”

Rosa shrugged. “You can stay with me. If you want.”

“Um,” said Amy. “That’s okay. I’m just—using the opportunity to spend a little extra time at the office, you know, put in some work on the ol’ backlog.”

“You don’t have a backlog,” Jake pointed out. “You’ve finished every case file on your desk, and yesterday I caught you trying to steal one of mine.” Amy looked away guiltily.

“Are you at all worried about this aggressive airborne spore thing?” broke in Terry, who was all twitchy about sickness and stuff ever since he’d had kids.

“Ooh,” Jake said, “let’s look up the symptoms on that website, uh, IMDb for germs—”

“Web MD,” said Amy, “and really, we don’t have to—”

“Gina can do it,” said Boyle, “since she’s already on her phone—”

“Sorry, guys, that’s _just not possible_ ,” Gina answered, without looking up from her screen. “I’m on a strict information-cleanse right now. No news, no Google, just brunch instagrams and photos of dogs that look like Mark Ruffalo.”

Terry paused. “How many of those can there possibly be.”

“Oh, Terry,” said Gina. “Oh, Terr-bear. You’re like a giant internet baby. Never lose your sparkle.”

“I really don’t think it’s anything to get concerned about,” Amy insisted. “The note from my landlord said it only affects 40% of the population—”

“Changed my mind,” Gina said, typing away furiously. “I forgot how suggestible Amy is, this is gonna be hilarious.”

“I’m fine,” said Amy. “I’m totally fine!”

“Stage one of an Estonian Fighting Mold infection,” Gina read. “Elevated body temperature—”

“Then it’s a good thing I feel totally _cool and collected_ ,” said Amy. For some reason, her idea of acting casual was to do everything in slow motion. As if moving underwater, she lifted her notebook and waved it, trying to discreetly fan herself. “Boy,” she said loudly, “Is it really... _cold_ in here?” Sweat beaded on her upper lip.

“Stage two,” Gina went on. “An itchy full-body rash.”

“Psh,” said Amy. “These symptoms are ridiculous.”

“You’re scratching your shoulder,” Rosa pointed out.

“Except I’m...not,” Amy said, dropping her hand and scratching at her shin with the toes of her other foot.

“Stage three: paranoia.”

“Well,” Amy gave a forced laugh. “That’s not a problem. In fact, don’t you think it’s a little paranoid to be sitting around watching me? How do I know you guys aren’t infected, hmm?”

“Stage four: uncontrollable rage.”

“STOP READING SYMPTOMS, I FEEL PERFECTLY GODDAMN FREAKING NORMAL,” Amy screamed, flinging a fistful of highlighters at the wall so violently that Terry dropped his yogurt.

There was a long pause.

**  
  
**

Amy came back from the doctor’s with a note saying she was fine. “Also,” she added, “the doctor told me I’m in the ninety-ninth percentile for medical suggestibility.”

“Are you proud of that?” said Rosa. “You understood that’s a bad thing, right?”

“What?” Amy’s brow furrowed. “Oh. Yeah. Of course, of course,” she said, but her startled cartoon deer eyes said otherwise.

Amy had this thing where she did stuff that normally would’ve annoyed the hell out of Rosa, except it didn’t annoy Rosa at all. Which was confusing. Also, annoying. “Anyway, she said I should find someplace else to stay for the time being.”

“Amy, you’re welcome to crash with me,” said Jake.

Rosa gave him a look. “Weren’t you saying last week your apartment’s borderline-unlivable?”

“I’ll have you know the mice are barely even a problem anymore,” Jake said with dignity, taking a slow sip of coffee. “Ever since that wave of rats came in,” he mumbled into his cup.

“What?” said Amy.

“Haha, classic _New Yawk_ ,” said Jake in a cartoony accent, spreading his arms wide. His body language collapsed in on itself like a sagging balloon. “Oh god it’s a nightmare,” he whimpered. “On the plus side, right now, there’s a fragile peace while the mice and the rats fight for dominance.”

“I, uh, think I’ll pass,” said Amy.

“That’s probably good,” Jake muttered. “Not sure how an outsider would affect the balance.”

Boyle frowned. “Jake, buddy, are you okay?”

Jake took another long swig of coffee. “Haven’t been sleeping much.” He stared into nothingness. “Did you know rats have a special scream that’s just for dying? And another one that’s just for killing?”

“It’s settled,” said Terry, turning back to his computer. “Jake rooms with Boyle, Amy rooms with Rosa, everybody gets the hell back to work and Terry enjoys his emergency backup yogurt in peace.”

Amy owned eight pounds of doilies.

Rosa had thought maybe moving Amy’s stuff in would be a hassle, but the whole process took less than half an hour. For one thing, Amy was a ridiculously organized packer. For another thing, there wasn’t any furniture to carry in; she had only brought the necessities.

The necessities for some reason included the doilies.

All eight pounds of them.

Rosa could not think of a purpose for even one doilie.

“So so sorry to put you out like this,” Amy kept saying.

Amy—and her suitcases and her crate of books labelled “books!” and her bag of toiletries labelled “toiletries!” and her box of office supplies labelled “office supplies!” and, yeah, the doilies—would be staying in Rosa’s weight room.

Rosa shrugged. “Whatever,” she said. She didn’t even use that room much. She lived on the first floor, and ever since she’d started lifting weights in view of the living room window, her building hadn’t been broken into or vandalized once. Apparently, people found her intimidating.

Heh.

“Still,” said Amy. “I swear I’ll try to keep out of your way.”

The thought of Amy getting in her way didn’t really bother Rosa. If Amy was gonna be staying a while, it was stupid to make her hole up in the weight room with all her possessions like a squirrel. She should feel free to wander the whole apartment and sit at the table and use the couch and stuff. Rosa didn’t mind. She owned more than one chair. They could eat breakfast together, or watch TV, or—what did Amy do for fun? Jigsaw puzzles?

“I really don’t care,” Rosa assured her. “And you can leave your shampoo and all that shit in the shower.”

“Okay,” said Amy. She shifted her weight awkwardly. “Uh, I’m gonna get settled in,” she said. “You can go—hang out in the living room? Or wherever! It’s your apartment!”

“Yeah,” said Rosa.

She was watching a special about sharks a few minutes later when Amy tiptoed behind the couch.

“Can I keep my kitchen stuff with yours?” Amy asked. Amy didn’t cook; her kitchen stuff was just a mug and an egg timer.

Rosa nodded. On the screen, a great white shark was keeping its cool around a guy in a scuba suit.

“Uh, hey,” Amy’s voice called through the doorway, “there’s an axe in this drawer?”

“Yeah,” said Rosa. “That’s my kitchen axe.”

“That’s—how can you tell it’s a kitchen axe, in particular?” said Amy.

“Because it’s—in the kitchen?” said Rosa slowly. Amy was normally very smart; maybe moving had stressed her out.

 

“I made you a hot cocoa, as a way of saying thank you,” Amy announced during the next commercial break. She was holding a mug in both hands, and her face was a mask of fortitude.

“Uh huh,” said Rosa.

“It—I think I maybe did a wrong step, somewhere,” Amy added. She handed the mug to Rosa. The liquid inside was thick and lumpy. There was a greenish film on it. Rosa took a sniff. It smelled like warm dog shit, but Amy was probably still freaking out about her building, and she was—trying to be nice, or whatever, so Rosa attempted a white lie.

“It...smells like regular shit,” Rosa said, as brightly as she could.

“Yeah,” said Amy. “I’m—actually pretty sure you shouldn’t drink that.” She took the mug from Rosa’s hands and disappeared into the kitchen.

“You could buy me a coffee,” Rosa called after her. There was the sound of a mug clattering into the sink, and then Amy’s head poked out of the door.

“What?” Amy said. “Not that I’m, I mean, I’m certainly not opposed, per se, uh, quite the opposite—of that, but it’s just—I wasn’t expecting, to—”

“Instead of cocoa, or whatever,” said Rosa.

“Oh,” said Amy, stepping back into the room. “Oh. Yeah.” She laughed. It sounded awkward, somehow. “Haha, of course. Just your usual—friendly coffee, between friends. Right, buddy?” She punched Rosa on the arm. She probably meant to show friendship, but there was enough nervous force behind the hit to actually hurt. Rosa only respected her more for it. “Just some city gals, getting coffee,” Amy continued. “Just—”

Sometimes Amy got weird and forgot how to stop talking for a while, and there was nothing to do but wait it out. It was part of Rosa’s day, familiar, like the rumble of the subway or the feeling of slipping on a well-worn pair of boots. Usually, Rosa didn’t—mind, or whatever. Usually. But if Amy called them “gal pals”, Rosa was punching a wall. She grabbed her jacket.

“Are we going?” said Rosa.

On the walk over, they talked about work, for a value of “making bets on the source of that smell coming from Scully’s desk.” Amy’s theory was either a long-forgotten ham salad sandwich, or a giant diaper.

“Why would—” But Rosa stopped herself. There was no answer to that question she wanted to hear. “Still can’t rule out that it’s coming from Scully himself.”

Amy considered this. “Sure, but how could we ever isolate the variables? We’d need to convince him to get out of his chair, and I don’t see that happening without some sort of brilliant, convoluted plan with a million moving parts and—”

“Or we set his chair on fire,” said Rosa.

“Terry said if we could go six months without anybody starting a fire in the building, he’d bring in smoothies,” said Amy.

“Santiago, if you burn Scully’s chair, I’ll bring in ice cream,” Rosa told her.

Amy tried not to laugh, but she did. Rosa smiled.

The bodega closest to Rosa’s apartment was her favorite bodega in the city, for three reasons:

  1. It didn’t try to be anything but a bodega.

  2. The guy who worked the register was just afraid enough of Rosa that he’d never tried to hit on her, but not afraid enough to stop being a smartass.

  3. They made their coffee with sweetened condensed milk. It tasted disgusting, but at this point, Rosa liked complaining about it more than she liked drinking good coffee.




 

“Hey, it’s Xena!” Sonny called when they walked in. The nickname thing was new. It was a mark against him. On the other hand: people not knowing her real name was a plus, so. A draw.

Rosa narrowed her eyes. “Wanna guess how many different ways I could break your arm?” she said.

Sonny shrugged. “Not sure why you’d need more than one. What’re you buying? Anything interesting?”

Amy glanced back and forth between them. “Two coffees? Decaf?”

“Sure,” said Sonny. “On the house.”

“Uh, really?” said Amy.

“When I say, ‘free coffee for life—’” Sonny said.

Rosa remembered him saying it, but she hadn’t thought he was serious. Amy raised her eyebrows, like, ‘Is there a story here?’

“You haven’t heard about this?” Sonny asked Amy. She shook her head. “So, my cousin’s kid hangs out here after school sometimes. Some older boys’ve been bullying her, all that shit. The other day, Xena here stops by for some gum, and while she’s in line, she starts teaching the kid self-defense moves. By the time Xena makes it up to the counter, little Claudia has learned how to break an attacker’s nose, five different ways to take a dude down, and all the major pressure points on the human body. Claudia’s in kindergarten, by the way. She came in crying, and now when she grows up, she wants to be a ninja.”

“Awwww,” said Amy, pulling a more misty-eyed version of the cartoon deer face. “That’s so _sweet_.”

Rosa wasn’t sure what to say to that. She hadn’t been trying to do anything. She just didn’t know how else to talk to kids.

“But the whole point was for me to buy you a coffee,” Amy added. She squared her shoulders. “I’ll have to buy you something else, then.” Her face lit up. “Spoon rests! I noticed when I was in your kitchen: you don’t own a single spoon rest.” She said it the same way someone would say, ‘you don’t own a toilet’ or ‘your house doesn’t have a roof.’

“They rest anywhere you put them,” said Rosa. “There isn’t different gravity for spoons.”

Amy scoffed and retreated to the back of the shop.

“I like her,” said Sonny. Rosa wasn’t impressed; only an asshole wouldn’t like Amy. “She your Gabrielle, so to speak?” Sonny wiggled his eyebrows. Rosa gave him a look. The same look had once made Jake hide in a filing cabinet for fifteen minutes. “Hey, don’t hate,” Sonny said, holding up his hands. “Just tryin’ to be less motherfucking heterocentric around here.”

When Amy returned a few minutes later with an armful of spoon rests, Sonny did a twitchy thing with his face like he was trying not to smile at Rosa.

“Genuinely didn’t know we carried those,” he said with a shrug, ringing them up. “Ten dollars.”

“That sounds cheap,” said Rosa suspiciously. Free awful coffee was one thing, but blanket discounts were a step too far.

Sonny sighed. “Welp, welcome to our going-out-of-business sale.”

“What,” said Rosa.

“There were a ton of signs by the door,” Amy put in.

Yeah, probably. Rosa had been distracted, because Amy had been laughing and smiling, and it was—distracting.

“What the hell,” said Rosa. When she thought about it, Sonny did seem less chipper and annoying than usual. Normally, he would’ve given her way more shit about Amy.

“Yeah,” Sonny said. “Health inspector came by last week. He hit us on a bunch of bullshit violations, charged us thousands in fines, and gave us a list of recommendations that were basically ‘you can stay open if you gut the inside of your building and start over from scratch’, which is weird because we passed last year’s inspection just fine and nothing’s changed.”

“That’s awful,” said Amy, eyes wide and earnest. “That—sounds like corruption, to be honest.”

Sonny nodded. “Yeah, it’s pretty clear they just wanted us gone. Insult to injury,” he added, “the new owners stopped in yesterday with fliers. Which is how we learned our replacement is an artisanal margarine shop. Or, sorry—” He held up a flier and read, in a pinched voice, _‘Marginalia: a craft margarine experience.’_ ” He started to laugh, but halfway through it collapsed into a sigh.

A craft margarine experience. Rosa felt a strong urge to break something.

“Amy,” Rosa managed through clenched teeth, “will you hand me a spoon rest?”

“Uh, are you gonna snap it in half?” said Amy.

“...nnnno,” Rosa lied, fists clenching.

“You know what,” said Amy, “actually I’m okay with you breaking a spoon rest, that seems like a relatively reasonable outlet for—uh, here you go.”

The spoon rest was ceramic. It came apart in Rosa’s hands with a satisfying crack.

“I’m so, so sorry,” Amy was saying to Sonny.

He wiped a hand down his face. “It’s fine, man, that thing’s her property now. Or maybe your joint property, but—”

“I meant about your store,” said Amy. “I wish there was something we could do to help—”

“I appreciate the thought, but I don’t think there is,” said Sonny. “Man, the rents already pushed us out of the Heights, so we move to the one corner of Brooklyn that looks immune to gentrification, only to get evicted for fancy margarine? It’s like, is any part of the world safe from hipsters? Where do we build our next store, the bottom of the ocean?”

“At least until the luxury party submarine takes off in 2030,” said Amy.

“Gina’s trend predictions are full of crap,” said Rosa.

“I don’t know,” Amy said, “She was right about Uber. She was right about the man-bun. She was right about the Canadian Prime Minister election, weirdly.”

“Here,” Sonny said, handing them each a coffee. “Take ‘em before they get cold.”

Rosa stared at the cup in her hand. The last of its kind.

She could feel Amy patting her on the shoulder. “It’s such a shame,” said Amy. “I can tell this place meant a lot to you.”

Rosa swallowed past the lump in her throat. She drew herself up to her full height. “Sonny—” she said hoarsely.

“It’s okay,” he said, “I know.”

“—your coffee is _disgusting_.”

“So I’ve heard,” said Sonny with a smile.

Rosa ran for the door, blinking hard.

“So,” said Gina. She was sitting on Rosa’s desk. Sitting on. The desk. Rosa narrowed her eyes, but it was hard to intimidate someone who wouldn’t look up from their phone. “What is it like living with Santiago?” Gina went on, “Did she set up a swear jar? Did she alphabetize your weapons? Are your belongings spontaneously turning into snow globes and cat-themed turtlenecks? What sorts of _comical shenanigans_ have befallen you two? C’mon, Mama needs her drama fix.”

Rosa gave her the ‘Jake Peralta you are only safe inside this filing cabinet’ face. Nothing. On second thought, maybe the look was specific to Jake. She let out a growl instead.

Gina jumped up. “Whoa, she-bear. Chill.”

“She’s fine,” said Rosa. “Don’t be an asshole.”

Because it was fine. It was totally fine.

Amy was an almost ludicrously considerate roommate. She cleaned up after herself. She didn’t eat any of Rosa’s food or use any of Rosa’s stuff. She didn’t play music or make much noise. Other than the spoon rests in the kitchen, there was no trace of her around the apartment. Any time she was home, she stayed in her room and kept to herself.

It was like rooming with a ghost. A ghost who lived on instant oatmeal and watched a lot of Miss Marple. (Rosa could hear it sometimes, very muted, on her way past the weight room. Often, it was the only sign she wasn’t alone in the apartment.)

There was no reason this should’ve been a surprise. What had she expected? Had she thought she and Amy were gonna hang out all the time? What, had she really pictured them eating breakfast together every morning, yawning and bitching companionably about how early it was? Had she assumed they’d eat dinner at the kitchen table—probably takeout, since neither of them cooked—sharing drunken noodles and stir fry and arguing over who got what fortune cookie?

Had she imagined they’d watch TV on the couch together afterward, sitting shoulder to shoulder and making fun of all the shit cop shows always got wrong, and then maybe sometimes Amy would fall asleep with her head on Rosa’s shoulder and her hair soft against Rosa’s cheek?

No. Obviously. That was stupid.

So: it was fine.

Rosa sat straight up in bed, rubbing her eyes. It was 3 AM, and there were noises coming from her living room.

Footsteps. A thump.

Shit: burglars. Thinking fast, Rosa did the only sensible thing: grabbed her mace from under the night stand, crept down the hallway, and ran through the door, yelling.

Silence.

Amy stood in the center of the room, fresh from the shower, wrapped in a towel. Rosa scanned the area. No intruders. Just Amy, who left her room so rarely that the sound of her moving around in any other part of the apartment had woken Rosa out of a sound sleep. She was in the middle of ironing something—the thump had been the ironing board, Rosa realized—but now she stared up at Rosa with wide eyes.

“Sorry!” Amy squeaked, like it was instinct. Her hair was still wet, and there were beads of water in her eyelashes. “I couldn’t sleep, and then I thought, y’know, I’d wind down with some quick ironing—“

Did Rosa own an iron? She wasn’t sure. Amy had probably brought one, though. Amy had probably brought one, and then a backup iron, in case anything happened to the first one. No doubt it was piled up in the weight room, along with the other boxes Amy hadn’t unpacked and wasn’t planning to, because this was all temporary, they weren’t roommates, they weren’t—

“What,” said Rosa, “in case your pajamas got wrinkled?”

“Um.” Amy ducked her head. “I’d already ironed my uniform, all my shirts, and all your curtains this morning, so it was slim pickings.” Her forehead furrowed. She set down the iron and coughed. “Hey, Rosa, um, is that a mace you’re holding? Like, a medieval spiked-ball-on-a-chain mace?”

What was Rosa supposed to say to that? Obviously it was a mace. “I thought I heard intruders.”

“I’m so sorry,” said Amy again, like Rosa was going to be mad at her for walking, or ironing or something. “I didn’t mean to disturb you—“

“You didn’t,” said Rosa. Amy gave the mace a dubious look. “I’m just not used to—“

“I have a sister,” Amy said suddenly. “You know, I can stay with her, if you’re—“

“It’s fine, Santiago.”

“Just—if this isn’t working out, I’m happy to find someplace else to crash, because, you know, I don’t want to jeopardize what we have—um, our working relationship, I mean—just because I—“ Amy broke off and looked at the floor. On the way down, her eyes paused for a half-second on Rosa’s legs. Rosa was wearing an oversized T-shirt, no pants, because she’d been sleeping, and because at this point the odds of running into Amy at home were basically zero. “Um,” said Amy. She swallowed.

Rosa was too tired for this shit. If Amy was that embarrassed to catch a glimpse of Rosa’s thighs, it was Amy’s problem. That was what happened when you only watched shows where all the heroes were seventy-year-old women.

“IT’S. FINE,” Rosa spat through clenched teeth.

The dubious look again. This time with a side of “sad Disney princess.”

“Are you sure it doesn’t bother you?” said Amy.

“I don’t care,” Rosa gritted out, turning back towards the door. The mace swung by her side. Somehow it felt heavier than before. “Christ, stay as long as you want. Or don’t. Nobody’s making you.”

“What?”

Amy sounded genuinely surprised. Rosa stopped walking.

“If you don’t want to stay,” said Rosa. “I’m not stupid.”

“Why would you think—“ Amy started. She broke off. “Oh.”

“Yeah,” said Rosa. Amy wasn’t stupid either. “Whatever.” She headed down the hallway.

“Goodnight!” Amy called after. “Uh, do you mind if I iron your dish towels?”

“What?”

“Oh,” said Amy, “it’s just—I had a good rhythm going, and it helps me think?”

Rosa sighed. “Knock yourself out.”

**  
  
**

Amy was waiting for her the next morning at the station with a fresh cup of coffee.  Rosa accepted the cup and took a sip. It tasted good. She was so used to her coffee being cloyingly sweet that she almost spat it out in surprise.

“Hey,” said Amy, “about that weirdness last night—“ Rosa drank more coffee, willing Amy not to apologize again. Amy took a deep breath. “I think we got off on the wrong leg,” she said. Rosa glanced up from the cup. “Foot!” Amy corrected herself, going pink. “The wrong foot. ‘The wrong leg’, that’s not even a thing.” She laughed for a half a beat too long. “ _Nobody says that_.”

“Okay,” said Rosa.

“I really do appreciate that you’re letting me stay with you.”

Rosa shrugged graciously. “Whatever.”

“Still,” said Amy. “It was really nice of you to—“ She cleared her throat. “So, I called in a favor with Terry, and he’s giving us two days to look into the situation with Sonny’s bodega, because there is definitely something shady happening there.”

“You don’t have to do that,” Rosa told her.

“And I talked with Sonny this morning,” Amy went on. “He gave me the name of the health inspector who shut them down. He didn’t remember the guy’s plates but he remembered the kind of car, and either government worker salaries have suddenly skyrocketed, or we have a crooked health inspector, because he’s got a limited edition Ferrari.”

“He could just be really good at money management,” said Rosa flatly. “Or really crappy at it. We don’t have enough to go on. You know that.”

“Cops have to listen to their gut sometimes, right?” said Amy, big brown eyes wide in appeal. “Doesn’t this feel fishy to you? Doesn’t it feel like we should do something?”

“It’s not enough,” Rosa repeated. “Doesn’t matter how it feels, you can’t fix everything, Santiago.” She took another sip. Since they’d started talking, she’d forgotten it was good coffee. This time, she spat it out in surprise.

“ _Gross_ ,” said Hitchcock.

“Shut up,” said Rosa.

“Hitchcock, are you scratching your back with a ham bone?” said Amy.

“Oh, _excuse me,_ ” Hitchcock said, “What, do you expect me to use the ham instead? ...because I can’t find it.”

 

 **  
** “Shouldn’t you be out there with Santiago, working on the margarine thing?” said Terry, rolling his chair up to Rosa’s desk.

Rosa didn’t look away from her screen. “Not enough to go on.”

“Santiago seemed to think—“

“Look,” said Rosa. “It sucks about that bodega. But that’s life. Bad things happen. Stuff doesn’t go how you want it to. Everything is terrible and there’s nothing you can do about it.”

“Uh, so,” Terry said brightly, and his voice climbed an octave the way it did whenever he thought he was being subtle, “how’s it going with you two sharing a place?”

She bit the inside of her lip. “Fine. Great.”

“Because you’re making the same face Cagney or Lacey makes when she needs to confide in me about something.”

“Your kids are _two_ ,” said Rosa. “How many secrets can they have?”

“Plenty,” said Terry. “Most of ‘em pertaining to Potty Time, but I’m guessing that’s not what’s going on here. Come on, Diaz. Are you and Santiago fighting?”

“No,” said Rosa. “We don’t see each other enough for that,” she muttered.

Terry nodded slowly. For some reason, he had a knowing look on his face. “Oh,” he said. “Yeah. About that.”

“I’m not talking to you about my feelings,” she said flatly.

“Okay,” he said. “So, I think—sometimes, when someone is giving you a lot of space, it’s because they have a problem with you. But sometimes, maybe it’s because they were worried about ruining an important relationship by coming on too strong and so maybe they asked, um, a trusted colleague for advice. And maybe he told her that she’d be fine as long as—“

“You told Amy to hide in her room and not talk to me?” Rosa interjected. “That’s messed up.”

“No,” said Terry. “I told her to leave you some breathing room and respect your boundaries. I didn’t expect her to take it to Santiago levels of overachieving.”

Rosa glared at him. “You didn’t expect Santiago to act like Santiago?”

“Sure, in hindsight,” Terry said.

“The store thing, it’s still a weak case.”

“Yeah,” he said, “and maybe it’ll be nothing, but you're both excellent detectives, so if she trusts her instincts, just this once, I’m willing to trust them, too. And Diaz? You were pissed she wasn’t spending time with you, and now you’re pissed she wants to work a case together?” Rosa studied the surface of her desk and said nothing. “When my girls are that unreasonable, we work through those messy emotions with fingerpainting,” said Terry, “but Terry’s not gonna make you do that, because we’re all adults here, and—“

“Quick,” Jake shouted, bursting into the room. He was wearing a baggy, stained tux and a fake mustache. “No big deal but does anyone know a magic trick? It’s _very important_ —“

Rosa and Terry turned to look at him.

“You know what, on second thought I can just use Google,” Jake added, grabbing his phone and bounding away. “Never mind, you guys, I’m Googling it!”

“Look,” said Terry, turning back to her. “Take a walk on your lunch break. Think it over. Also, remember that I’m your boss and this is not a buffet where you get to pass by cases whenever you damn well please. Let’s treat your job with the dignity it—”

“And, uh, nobody look in the parking lot for the next five minutes!” Jake yelled as he retreated. “No reason! Okay, bye!”

**  
  
**

Rosa didn’t live that far from the station. When she left for lunch, she rode her motorcycle back to her apartment and went for a walk in her neighborhood.

She passed the laundromat. She passed the people with the goddamn dog who was always barking. She passed the spot where she’d once tackled a mugger. She passed the other laundromat. She passed the place where Sonny’s bodega had been.

MARGINALIA: LAUNCH PARTY said the sign in the window. Music blared from inside. A line of pale, jittery-looking hipsters snaked around the corner. A guy in a shiny suit, a backwards baseball hat, and annoying shades stood in the door with a tray of samples.

“Hey, lady,” he called, “how about a free taste of our signature Marge-arita, on the house? That’s an authentic margarita, infused with our small-batch margarine and—“

“Stop talking,” said Rosa, “or I’ll ram that sample cup through your ear canal.”

He laughed. “Oho, sorry, didn’t realize it was that time of the month! In that case, can I interest you in a Skinny Marge? That’s our signature Marge-arita, but made with a low-cal sweetener and with a Mocha Marge boost, available as a $1 Add-It-On for a limited—“

**  
  
**

Amy was back at her desk when Rosa returned.

“I’m in,” said Rosa, still pushing the hair out of her eyes from the ride over. “Let’s do this.”

“Yes!” Amy jumped up from her chair and pumped her fist. “Loving the enthusiasm!”

“Let’s destroy those sons-of-bitches,” said Rosa. “Let’s bring their crappy enterprise to its knees and make them cry.”

“...with some caveats, still overall feeling okay about the enthusiasm!” said Amy.

Rosa settled into Jake’s empty seat. “What’ve we got so far?”

“First of all,” said Amy, “so, this may not be anything, but last night I happened to be researching the family trees of your local city council members—“

“Wow,” Gina broke in from across the room, “even for you, that is sad. Is it possible to hold an intervention just for boringness? Get a hobby, Amy. Buy into a conspiracy theory. Develop a tragic gambling addiction. Tattoo or pierce _something_ , it’s for your own good.”

“Oh, _har-di-har_ ,” said Amy, rolling her eyes, “For your information, I was looking for something dull, because I was trying to go to sleep after a really intense episode of  _Murder She Wrote_. But so, Councilman Greer—“

“Gonna stop you right there, girlfriend,” Gina broke in. “You have a solemn duty, both to Rosa and to anybody else who may or may not be eavesdropping, to get to the point.”

“Tommy Greer, the guy who opened Marginalia, is Councilman Greer’s nephew,” Amy said. “Now, that in and of itself doesn’t necessarily—“

“Wait,” said Rosa. “Sonny’s cousin is running for city council. I think he’s running against Greer.”

“What?” said Amy. “Oh my god, why didn’t you mention that before?”

Rosa looked at her. “Because it’s city council and nobody cares?”

“Okay, number one: remind me to put together a PowerPoint about the importance of local elections,” said Amy breathlessly. “Number two: I think we may just have our first lead.”

 

 

Rosa spent the rest of the day gathering information. When she got back home, Amy was typing at the kitchen table.

“Hope you don’t mind that I set up in here,” said Amy. “Thought we could compare notes.” She’d spread her papers all over the surface of the table. She looked comfortable there. She looked natural.

“That’s cool,” said Rosa.

It was.

“So, I did some digging,” Amy said. “And since Greer was elected, the number of bars or restaurants in your ward that closed suddenly for health code violations has more than quadrupled. Weird, right?”

“That pizza place with the dumb name—” said Rosa. She blinked mournfully.

Amy pointed to a sheet of looseleaf crammed with words. “On the list,” she said. “And at least three of them had some kind of dispute with Greer beforehand.”

“Health inspector’s a dead end,” Rosa added. “He’s only been working here a month. Tailed him for a while, didn’t find anything.”

“Tomorrow, I’ll follow up with as many of the other former restaurant owners as I can find,” said Amy. “Establish a pattern.” She sighed.

Rosa knew what she was thinking: bribery was hard to prove.

“If we do find a pattern, what’s the next step?”

“I have some thoughts on that,” Amy said. “A lot of thoughts.” She frowned. “Hey, are you hungry?”

“Wanna order some Thai?” said Rosa.

“Sure,” said Amy. “Thai sounds good.”

It really did.

**  
  
  
**

“Something’s still bugging me about that margarine store,” Rosa muttered on their way into work the next morning.

“Is it the very existence of a margarine store?” said Amy.

“There was a line out the door,” said Rosa. “Have you ever heard anyone give a shit about margarine before?”

Amy shook her head. “Think we’re looking at a front?”

“What are the odds people suddenly give a shit about it now?”

Amy froze in her tracks. “There’s one way to be sure,” she said slowly.

She was right. Rosa knew she was right. Rosa had realized it first, what they’d need to do. That didn’t make it easier.

“I can do it,” said Amy stoically. So ready to jump on the grenade, and it wasn’t even her neighborhood.

‘ _You’re amazing,_ ’ thought Rosa, out of nowhere. She wasn’t trying to think it or anything.

Huh.

Suddenly, a lot of shit made sense.

“No,” Rosa said. “I’ll do it.”

Amy’s eyes welled with concern. “Are you sure?”

“I’m sure.”

**  
  
**

Rosa clenched her teeth. She took a deep breath. She thought about Sonny. She thought about the neighborhood. She thought about free shitty coffee and Amy’s impossibly earnest face and the word _marge-arita_. The stakes were high enough. It was worth it. She could do this.

“Boyle,” she willed herself to say, “I need to talk to you. About food trends.”

**  
  
**

“What’d you discover?” Amy asked an hour later.

“Artisanal margarine’s not a thing,” said Rosa. She stared into space. The wall blurred. “He also told me what is big in the food scene.” Bile rose in her throat, and she swallowed it down again. “Pig rectums,” she said. “It’s pig rectums, Amy. Deep-fried pig rectums. He—”

Amy patted her shoulder and made soft sounds of empathy.

Rosa’s nostrils flared. Her jaw quivered. “He _used the word ‘velvety’._ ”

“You’re a good detective,” said Amy soothingly.

Worth it, Rosa told herself. It got a little easier to believe as Amy's patting became more of a back rub. Worth it.

**  
  
**

“Hey,” said Jake a little later, when Rosa had taken some deep breaths and drank a glass of water and brushed her teeth five times in the employee bathroom. “Got a possible lead on your case. I collared a mid-level drug dealer fifteen minutes ago. The perp’s not talking yet, but the trunk of his car is telling a different story.”

“Okay,” said Rosa.

“Just—I wanna be clear,” he said in a rush, dropping the macho persona the way a person might drop their keys. “The stuff in the trunk is what’s telling the story, not the car that—it’s not a talking car.” His eyes widened. _“At least, as far as we know.”_

“What’s in the trunk, Peralta,” she snapped.

“It was littered with little plastic tubs from Marginalia,” said Jake. “Empty, but. At least thirty of them.” 

“Nothing adds up,” said Boyle behind him. “Driving around with thirty pounds of butter, I can see—”

“Can you, though?” said Jake.

“—or thirty pounds of lard, that makes _sense_ ,” Boyle continued, waving his tiny arms around for emphasis. “Even thirty pounds of shortening if he was baking pies en masse—”

“The ‘meth dealer with a side business in pastry’ thing, that’s not my theory,” Jake added in an undertone.

“—but margarine?” Boyle’s eyes were starting to bug out of his head. “Margarine, mankind’s greatest folly?”

“Jesus, Boyle,” said Rosa.

“Sorry,” he said, “ _humankind’s_ greatest folly.” He coughed. “How would you even use that much?”

“Boyle, we’re pretty sure Marginalia’s a front,” Amy said. “The containers are just what they were using to move their drugs in.”

“Oh,” said Boyle. “Yeah, that—does check out.”

“So,” said Jake, “are we raiding a meth lab?” He grinned. “Ooh, I get to pick the music on the drive there! Last meth case, I put together an awesome drug bust playlist.”

Amy made an aggrieved face.

“Santiago,” said Rosa, “wanna ride with me?”

“Yes, please,” said Amy.

**  
  
**

It was a pretty typical meth lab raid.

Tommy Greer’s lackeys had guns, which wasn’t surprising. They were too jumpy to be good shots. Also not surprising.

The goal was to take them out before they did anything stupid, like cause collateral damage or ignite the mounds of dangerous chemicals. Things went pretty much to plan, although there was a part where two guys came at Rosa at once, and Amy took one of them down by slicking the floor with a sample marge-rita.

Jake probably shouted a one-liner about it. Rosa was too busy punching the other guy to be sure.

**  
  
**

“How was it?” Gina asked back at the station.

“An action-packed free-for-all so exciting and visually stunning that words will never begin to capture it,” said Jake.

“I meant, did any of you get a dramatic scar?” said Gina. “Or have one of those near-death experiences where you realize what really matters and decide to donate all your savings to worthy causes, like my dance team’s emergency fund?”

“What’s the emergency?” said Terry.

“We want new leotards.”

“I’ve been to your apartment,” said Rosa. “You already own an absurd number of leotards.”

Gina sniffed. “It’s like none of you even know what dance _is_.”

Terry looked around. “Anyone else hungry?” he said.

“Literally nobody else,” said Amy.

**  
  
**

**Two weeks later**

“Talked to the hazmat guys,” said Rosa after dinner. “They said the building’s safe for people again. Brought the price way down, though. Sonny’s trying to re-open by the end of the—are you washing the chopsticks?”

“What?” Amy turned around from the sink. “You never know when you might need—”

“Used disposable chopsticks?”

“Your only kitchen implements are a knife, two cereal spoons, and an axe,” said Amy.

“Fair.” Sooner or later, Rosa needed to buy a second knife. “We can store them on one of the spoon rests,” she said. At this point, she owned way more spoon rests than spoons.

“Can you help me dry these?” Amy asked.

“You do realize stuff dries in the open air if you let it sit there,” said Rosa, but she grabbed a dish towel anyway. It was weirdly crisp, so Amy had been stress-ironing. “Sucks that we couldn’t make the bribery charges stick.”

Councilman Greer kept insisting that he’d never known about the meth thing. The rest of it, they still couldn’t prove.

“Boyle let all the food blogs know about the restaurants Greer seems to have shut down,” Amy said as she scrubbed a cup. “It’s getting picked up by local press. People are upset. It could really hurt his chances next election.”

Rosa dried the plate. She looked in the sink. There was nothing else to dry. She set down the towel. Neither of them said anything for a few seconds.

“So,” said Rosa, “that’s that.”

“Listen,” said Amy. “I—oh god, I had a whole speech prepared, I had all the bullet points written out on notecards, and then I thought that trying too hard just caused problems last time, so I should probably, you know, do this off the cuff, play it cool—”

“Say it however you want to say it,” Rosa told her.

Amy nodded. “Yeah, okay, in that case, let me find the notecards, and— _augh_ , no, this is ridiculous. I can just tell you.”

“Okay.”

“Okay,” said Amy. “I—before, when I was kind of trying to avoid you, it was nothing personal. It was just—”

“Terry told me,” said Rosa.

Amy stared at her. “He—what did he tell you?”

This was treading suspiciously close to talking about feelings. Rosa sighed. “He told you to give me space.”

“Yeah.” Amy took a deep breath. “I didn’t realize you’d take it personally. I know I can be a lot to deal with—”

“Compared to what,” said Rosa flatly. Amy didn’t store rotting meat in her desk drawer and she’d never accidentally set her own sleeve on fire trying to send a fax. She was weird as hell, but she was a good cop. She was smart and tough and not a sociopath and—Rosa’s chest hurt.

“Just, you know,” said Amy, “I’ve heard from more than one ex that living with me could be kind of an ordeal?”

“Who,” said Rosa. “Who are these people. What are their names and addresses and approximate levels of combat skill.”

“Um,” said Amy.

Rosa couldn’t see any way around it just spelling it out. "You’re my friend.”

“Um,” Amy said again. “The thing about that. Is, of course, of course we’re friends. But before we started, you know, living together, I was in the early stages of considering asking you out?”

“Oh,” said Rosa.

“On a date,” Amy added, like it needed clarifying. “And I know, it would be complicated, because we work together. And I’m not even—I’m not saying you this with any expectation, I just thought you had a right to understand the situation, if you’re still okay with me staying with you—because it’s okay if you’re not—but I figured you should know that before you decide to do things like not wear pants around the apartment.” She swallowed. She was still holding a kitchen sponge in one hand. Rosa took it from her and set it on the counter. “You know,” Amy finished, “for instance.”

“Uh-huh,” Rosa said. Then she leaned in and kissed her.

Amy acted very surprised for a second or two, but then she got with the program. She was smart.

“So,” Amy said, as breathless as she got talking about the importance of voting for city comptroller or whatever. “Does this mean—”

At that point, only an idiot would have risked any degree of ambiguity. “Let’s go on a date,” said Rosa.

“Okay,” said Amy, with a small, pleased smile that was obviously a reason to kiss her again. It just was.

When she pulled away, Rosa could feel the corners of her own mouth tugging up. “I’ll buy you a coffee,” she said.

**Works inspired by this one:**

  * [[Podfic of] Margin of Error](https://archiveofourown.org/works/8493292) by [blackglass](https://archiveofourown.org/users/blackglass/pseuds/blackglass), [daroos](https://archiveofourown.org/users/daroos/pseuds/daroos), [exmanhater](https://archiveofourown.org/users/exmanhater/pseuds/exmanhater), [klb](https://archiveofourown.org/users/klb/pseuds/klb), [reena_jenkins](https://archiveofourown.org/users/reena_jenkins/pseuds/reena_jenkins), [Shmaylor](https://archiveofourown.org/users/Shmaylor/pseuds/Shmaylor), [swiiftly](https://archiveofourown.org/users/swiiftly/pseuds/swiiftly)




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